The embedding of vacuum interrupters in epoxy is a well tested technology. In this technique, the filling pressure is low and it will not cause damage to the vacuum interrupter. Furthermore, the force on the electric terminal is also not critical and no special fixation is needed. However, the filling time and curing time are relatively long.
Injection molding of thermoplastic material is used in this field of technology.
During the injection molding, the pressure in the cavity of the mould is very high during the filling and packing period. The vacuum interrupter will experience the very high pressure, and special attention should be paid to the metal cover area.
By using injective molding method with thermal plastic material instead of epoxy material to embed the vacuum interrupter inside the insulation material, the difference between these techniques is the pressure value applied to the insert. In general, in reactive epoxy molding situations, the pressure is from several bars to maximum 20-30 bars. At this pressure level, it will not result in high force and stress for the current connection and for the vacuum interrupters. Therefore, no special constructions are needed to protect the vacuum interrupters and also no special fixations are needed for the upper terminal. In this case, the filling time and curing time is relatively long.
In injection molding for vacuum interrupters, the maximum pressure could reach several hundred bars. The end metal cover of vacuum interrupters has a thickness of several millimeters which could not withstand such high pressure. At the same time, the resultant forces on the upper terminal are very high. Therefore, a very strong construction and fixation of the upper terminal in the cavity and protection for the end metal cover of vacuum interrupters are needed, in order to avoid deformation of it. In this case, due to the very high pressure, the filling and packing time is very short.